This qualitative case study examined how volunteer tutors are interacting with at-risk adolescent ELL students in one-on-one tutoring sessions. This study also investigated how volunteer tutors are supporting vocabulary acquisition within tutoring sessions with adolescent ELLs. As a non-participant observer, I used ethnographic methods, including observations, interviews, and document analysis to understand how three tutors were interacting in sessions and how they were supporting vocabulary acquisition over seven weeks. The following questions guided the research: How do volunteer tutors interact in one-on-one tutoring sessions with at-risk adolescent ELLs? How are volunteer tutors supporting vocabulary acquisition for adolescent ELLs in one-on-one tutoring sessions? Data were analyzed to determine how volunteer tutors were interacting in sessions and supporting vocabulary. Six themes emerged to explain how tutors were interacting in sessions and three ‘a-priori’ themes explained how tutors were supporting vocabulary acquisition. The results of this study are used to inform schools who institute volunteer tutoring programs for at-risk populations, researchers interested in vocabulary acquisition and adolescent ELLs, and faculty or staff members who work with at-risk populations. Furthermore, recommendations for future research are discussed for the field of education. / Literacy & Learners